Traffic cycle split selectors



March 24, 1970 G. D. HENDRICKS 3,503,040

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G. DONALD HENDRICKS M 746 a 8 SHOWN IN CROSS STREET GREEN United StatesPatent 3,503,040 TRAFFIC CYCLE SPLIT SELECTORS George Donald Hendricks,Campbells Island, Ill., assignor to E. W. Bliss Company, Canton, Ohio, acorporation of Delaware Division of application Ser. No. 534,603, Feb.10, 1966, which is a continuation of application Ser. No. 343,182, Feb.3, 1964, which, in turn, is a continuation of application Ser. No.742,160, June 16, 1958. Divided and this application Oct. 5, 1966, Ser.No. 619,080

Int. Cl. G08g l/08 US. Cl. 34035 4 Claims ABSTRACT OF THE DISCLOSUREThis application is a division of my copending application, Ser. No.534,603, filed Feb. 10, 1966, which in turn is a continuationapplication of my copending application, Ser. No. 343,182, filed Feb. 3,1964, which is a continuation of my application, Ser. No. 742,160, filedIune16,1958.

This invention relates to a tratfic control system and more particularlyto a traffic control system of the computer type able to select the mostexpeditious balance between main street and cross street use of a groupof intersections.

The invention comprises part of a trafiic control system which changesthe traffic signals at various intersections according to a pattern. Thepattern includes a right-of-way interval a caution interval, and a stopinterval for each street and is called a cycle. The invention providesmeans for apportioning the cycle between two or more intersectingdirections. The division of the cycle between the intersectingdirections of travel is here referred to as the split. When expressed asa percent division of the cycle between main street and cross street itis defined as a percentage split.

Heretofore, the percentage split of time available to main street and tocross street has been preset by hand or by time clock. Single dialpretimed controllers are normally set by hand to allow the mostefficient flow of traffic across the intersection. An interconnectedgroup on single dial controllers, all with the same cycle length,usually employed the same cycle split to allow most eficient progressionalong the main thoroughfare. Little flexibility was possible with thistype of equipment.

Multiple dial pretimed controllers were developed to overcome this lackof flexibility. With the usual three dials, three different percentagesplits were available, set in many cases to favor cross street trafficon one dial, to favor main street traffic on another dial, and balancedtrafiic on a third dial. Other common settings favored both streetsequally on one dial, main street on a second dial, and main street moreon a third dial. Dial changes were made at predetermined times usuallyby a time clock arrangement energizing control conductors and effectingremote dial change.

Another form of split change device in use today is shown in UnitedStates Patent No. 2,815,410 and con- 3,503,040 Patented Mar. 24, 1970sists of a number of contact assemblies associated with and positionedabove a dial unit. Keys are positioned around the dial periphery, onekey for each split percent desired. A remotely controlled transferdevice makes one contact assembly and key effective at one time andanother contact assembly and key effective at another time. The numberof split percentages available is limited by the size of the contactassemblies to three or four splits. A master programming devicedetermines which split is effective at various hours of the day.

Still another form of split change device is incorporated in and made apart of a cycle length change device and disclosed in United StatesPatent 2,761,119. Two adjustable frequencies are employed to vary themain street and cross street right-of-way periods. By increasing onefrequency the right-of-way period for the street is lengthened. In ordernot to change the total cycle length the other frequency must bedecreased to shorten the right-ofway period on the opposite street. Thissystem is costly to produce and maintain because in addition to thenormal amount of equipment required, two variable frequency generatorsare required at the master, an amplifier'is required at each localcontroller, and a three conductor cable is required to connect themaster with each local controller.

The invention does not require variable frequency generators oramplifiers and does not need more than two conductors to eachcontroller.

Traffic actuated controllers are not concerned with percentage splitexcept under certain circumstances. A two street controller with trafficdetectors in the cross street normally dwells in main street green andgoes to cross street green only on call. If cross street trafiic isheavy or if the recall switch is closed, the controller will operate asa cyclic controller with the cross street green interval being timed byits maximum timer and the main street green interval being timed by itsmini= mum timer. The setting of these timers determines the split at oneintersection.

A two street controller with traffic detectors in both streets maylikewise time as a cyclic controller if trafiic from both directions isheavy or if both recall switches are closed. Isolated actuatedcontrollers find their own best solution to the split problem, and arenot primarily concerned with this invention.

The full value of the invention is most evident when used in conjunctionwith a system of pretimed controllers. However, the invention operatesequally well when used with a system containing both pretimed andtraiiic actuated controllers.

The principal feature of the invention is automatic control of thetrafiic cycle split at a group of intersection traflic signalcontrollers on a grid or along a thoroughfare according to the densityof traiiic in intersecting directions as measured at one or morerepresentative intersections. Methods have been described above toremotely change the split at a number of intersections but non makes useof traffic density in the two intersecting directions as measured at oneor representative intersections during a number of traffic signalcycles.

What is believed to be new is a trafiic density com parator device ableto compare the ratio of measured traffic volumes in two intersectingdirections against a plurality of preset, adjustable ratios and selectone of a plurality of splits for the heavier direction of trafficdependent upon which of the preset ratios the measured ratio exceeds.The invention selects the most eflicient split of the cycle withoutvarying the overall duration of the cycle. The duration of the cycle maybe determined by factors other than the ratio of traflic densities inintersecting directions.

Trafiic density is here defined as the number of vehicles passing agiven point during a predetermined interval. Control of trafiic cyclesplit according to traflic density has a decided advantage over presetcontrols because the former system is related to actual rather thanpredicted traffic conditions. For this use a novel tralfic densitycomputer has been designed. The system for computing trafiic density,herein described, is considered superior to known systems.

One traffie computer and control system known in the prior artdetermines traffic density during a discrete interval, then selects thecycle length at the end of the interval, and operates on that cyclelength for at least one interval. At the end of each interval the countis erased. Actuations are then totaled during the ensuing interval. Thedensity thus computed is referred to as a discrete density or average. Adevice for determining such a discrete average is disclosed in UnitedState Patents 2,288,601 and 2,834,001.

A computer device is herein described which appears to be more accuratefor control work than any known device. It consists of a traflic densitycomputer which integrates traflic actuations over a running interval sothat the most recent actuations are given more weight than pastactuations. The count is not erased all at once but is allowed to drainoff as time transpires. This count approximates actual traflicconditions as nearly as is practical. An integrator and controller whichapproximates traffie conditions more closely than this would tend toover control or to hunt.

Since the running average of trafiic density is based on signalsoriginating from passing vehicles it is essential that the signalscreated by each passing vehicle be modified to be identical regardlessof the speed of the vehicle or the condition of individual detectors indifierent lanes. One of the features of the invention is a novel circuitwhich converts the signals received from several detectors into uniformsignals. The uniform signals are applied to the tratfic densitycomputers which consist of a capacitor charging circuit which permitsthe running average of trafiic density in each direction to berepresented by electrical potentials.

The potentials indicative of traffic in intersecting directions areapplied to a balance detector. Here the higher potential determineswhich direction of trafiic is to be favored. A potential divider reducesthe high potential by several preset ratios and then compares thesereduced values with the lower potential. This comparison determines theextent to which the direction of trafiic selected by the balancedetector is to be favored in the split.

In accordance with the present invention, there is provided a method oftratlic control for controlling traflic in at least two directions oftraflic flow and comprising the steps of: providing trafiic signallights for the two directions of traffic flow; electrically detecting acharacteristic of traflic in the two directions; developing electricalsignals representative of a characteristic of trafiic in the twodirections of trafiic fiow; electrically reducing the characteristicsignals to a ratio relationship of said characteristic signals;electrically comparing the ratio relationship with a referencerepresentative ratio relationship of traffic characteristics; and,controlling the traific flow in the two directions by changing theoperation of the trafiic signal lights when the ratio relationship isdifferent from the reference representative ratio relationship.

The principal object of the invention is to provide a system for thecontrol of traific cycle split at a plurality of intersections accordingto relative traffic densities measured at one or more representativeintersections.

It is another object of the invention to provide traflic densitycomputers for main street and for cross street, and a cycle splitselector consisting of a balance detector to determine which street isto be favored, and a group of ratio detectors to determine the ratio oftraflie in the two directions.

It is another object of the invention to provide a local split selectordevice able to select four splits at each intersection and operable overa two conductor cable.

It is another object of the invention to provide a split selectorapparatus able to select various splits relative to trafiic density ontwo intersecting roadways.

It is another object of the invention to select one of a series ofsplits to obtain most expeditious traffie flow on both the cross streetand the main thoroughfare.

It is another object of the invention to provide a split selector devicecompatible for use with other devices of similar design which selectcycle lengths and offsets.

The apparatus will be explained in detail with reference to thefollowing figures, in which like symbols are carried throughout thedrawings:

FIGURE 1 is a diagram showing a series of intersections along athoroughfare, trafiic detectors in each street at one intersection, amain street computer, a cross street computer, a split selector, slaverelays, and an interconnecting circuit to local controllers;

FIGURE 2 is a diagram showing a grid of intersecting traflic lanes,trafiie detectors in representative lanes, a north-south traflic densitycomputer, an east-west density computer, a split selector, traflicsignals at each intersection, and local traflic signal controllersconnected to the split selector by slave relays and an electric cable;

FIGURE 3 is a block diagram of a computer showing a number of blockingoscillators, a bistable multi-vibrator, a monostable multi-vibrator, aninstantaneous integrator, a long time integrator, percent trafficdensity meter, and an output terminal, approximate wave shape at eachstage is shown;

FIGURE 4 is a block diagram of a balance detector and ratio detectorsfor the thoroughfare system shown in FIGURE 1;

FIGURE 5 is a wiring diagram of the apparatus shownin FIGURE 4;

FIGURE 6 is a block digram of a balance detector and ratio detectors fora grid system;

FIGURE 7 is a block diagram of a balance detector and ratio detectorsfor a balanced grid system as shown in FIGURE 2;

FIGURE 8 is a wiring diagram of a split selector apparatus in a localcontroller; and,

FIGURE 9 is an isometric view of a two dial local controller.

General description The main street and cross steet trafiic densitycomputers are disclosed fully in US. patent application, Ser. No.738,327, filed may 28, 1958, entitled Traiiic Lane Control, but will bedescribed here in block diagram form for the sake of completeness. Inthe application named above, the computers are associated with detectorsin the inbound and the outbound lanes of main thoroughfare for detectingcharacteristics of trafiic, such as traific density, and are used tocompute inbound and outbound traflic density. Here, the computers areassociated with main street and a cross street and are used to computetrafiic density in the two intersecting directions.

Each traflic density computer develops a direct current output potentialsubstantially proportional to the running average of traffic density onthat street. Each computer contains an integrator circuit which averagestrafiic flow over a running interval of time. Heretofore, computerscounted the traflic flow over a discrete interval, totaled the countafter a fixed time, and erased the total at the end of the interval.This invention utilizes a running average which appears to approximateaverage traflic conditions more accurately, and leads to more accuratecontrol of traffic.

The output of each computer, a DC potential substantially proportionalto traflic density on that street, is fed to a comparator device whichconsists of a balance detector and a group of ratio detectors. A stageof preamplification may be inserted ahead of the balance detector toreduce the back effect on the computers.

When the balance detector senses an unbalanced condition it energizes arelay that switches the input potentials to a group of ratio detectors.The higher potential is reduced by a plurality of potential dividers andthe resulting reduced potentials compared with the lower inputpotential.

Each ratio detector, when unbalanced by the higher potentialrepresenting a certain ratio of main street to cross street trafiic,energizes a split selector device representing the best percentage splitfor that ratio of traffic. The split selector in turn energizes acontrol conductor leading to each local intersection controller toeffect the proper split at each intersection.

Main thoroughfare controlled system One application of the invention isshown in FIGURE 1. A series of street or highway intersections are shownalong a main thoroughfare. The local traffic signal controllers at eachintersection are electrically interconnected with a control circuit topermit control of the cycle split for most efiicient flow of trafiic onboth the main thoroughfare and on the cross streets.

At one representative intersection traffic actuated detector devices arelocated in, on, above, or along the lanes in both streets. In thisdescription pressure sensitive traffic detectors are used because theyare easy to represent and describe. However, any of the well known typesof detectors may be used without departing from the spirit of theinvention.

A representative intersection is chosen for most efficient operation ofthe system. The intersection may not be the one along the controlledthoroughfare which has the most tratfic; it would preferably be theintersection where traffic conditions most nearly approximate those atother intersections during most intervals of the day.

It is important to the accuracy of the system that detectors be locatedin all heavily traveled lanes at the representative intersection andpreferably in any other lanes frequently used. Lanes not detected reducethe accuracy of the tratfic density computers.

As shown in FIGURE 1, the main street MS is provided with detectors D1,D2, and the representative cross street RCS is provided with detectorsD3, D4. Each detector D1 to D4 consists of two plates mounted in thepavement, the bottom plate being electrically and mechanically grounded,and the upper plate insulated from ground. Upon passage of a vehicleover the upper plate of the detector D1, for example, a circuit isestablished to ground over conductor 1. Passage of a vehicle over eithermain street detector D1, D2 grounds a circuit in the main street trafficdensity computer MC through conductors 1, 2. Passage of a vehicle overeither cross street detector D3, D4 grounds a circuit in the crossstreet traflic density computer CC through conductors 3, 4.

Both traflic density computers MC, CC receive signals from theirrespective detectors, amplify the signals, reduce the number of signalsby a factor of two, give the remaining signals a definite duration,integrate the number of signals over a short interval, again integratethe number of signals over a long interval, and develop a direct currentpotential proportional to the running average of trafiic density on thatstreet. The function of the integrators is explained more fully inanother section.

The output of the trafiic density computers is available for a varietyof purposes. In the present invention, the outputs are used to selectthe proper division of traflic cycle time to main street and to crossstreet. In another system the outputs might be used to determine trafiiccycle length; in another application they might be used to provide aprogression; or any combination of these functions.

In this invention the computer outputs are applied to a split selectorSS comprised of balance and ratio detectors which compare the values ofthe potentials and permit the higher potential to energize a switchingdevice. The switching device routes the higher potential to the ratiodetectors through one or more potential dividers. It also routes thelower potential to the other side of the ratio detectors. The ratiodetectors compare the higher potential, reduced by the potentialdividers, with the lower potential to determine the ratio of main streetto cross street traffic density.

A ratio detector will become energized if the reduced higher potentialis greater than the lower potential. The ratio detector carries contactswhich switch power to slave relays SR which translate the informationreceived over three or four conductors to information capable of beingsent over two conductors IC to the local controllers LC. It is necessaryto reduce the number of control conductors required so that the cost ofinterconnecting cable will be kept to a minimum. In most installations acable already interconnects the various local controllers with a mastercontroller located at a central station. The split control function isassigned to two of the conductors or its control signal is superimposedon one or more of the conductors being used by a non-interferringcontrol function. A radio or other link might be employed to transmitthe information to the local controller.

Grid system The usual layout of a city may include a number of streetslying in east-west direction with a number of intersecting streets lyingin a north-south direction. To adjust the traffic cycle split at all theintersections to the average densities of traffic at all of the manyintersections, a few intersections that seem most typical are selected.Vehicular traffic moving east and west at these few intersections isused to determine one density. Vehicular traflic moving north and southat these few intersections is used to determine the other density.

In FIGURE 2 any street bearing eastbound traffic is designated ES; anystreet bearing westbound trafiic is designated WS. Streets normal to ESand WS streets are designated NS and SS. The streets are shown asone-way thoroughfares but may be the more common two-way streets or anycombination thereof.

Each signalized intersection is equipped with a local trafiic signalcontroller LC which may be either pretimed or traffic actuated or anycombination thereof. For purposes of illustration, pretimed controllersare used. To simplify nomenclature, streets running one direction willbe termed east-west streets and those running at right angles will betermed north-south streets.

On one or more representative streets in each direction traffic actuateddetector devices D1 to D3 are located in,

on, above, or along the lanes of travel. Pressure sensitive tratficdetectors are used by way of illustration but any of the well knowntypes of detectors may be used.

The streets chosen for trafiic sampling purposes must preferably berepresentative of the major portion of streets running in thatdirection. In FIGURE 2, one-way streets are illustrated with traflicdetectors in each lane of eastbound ES, westbound, WS, northbound NS,and southbound SS streets. To count most accurately and to anticipatechanging traific conditions it is preferred that the traffic detectorsbe located at the entry points to the grid.

Each of the east-west trafiic detectors D1 to D4 feed into individualcircuits of the east-west traffic density computer MC. Each of thenorth-south trafiic detectors D5 to D8 feed into individual circuits ofthe north-south tratfic density computer CC. It is important to theaccuracy of the system that detectors be located in all heavily traveledlanes and preferably in all other lanes frequently used in therepresentative streets. Lanes not detected reduce theaccuracy of thetrafiic density computers.

Passage of a vehicle over any east-west street detector D1 to D4 groundsa circuit in the east-West traffic density computer MC over conductor 1to 4. Passage of a vehicle over any north-south street detector D5 to D8grounds a circuit in the north-south trafiic density computer CC overconductor 5 to 8.

The function of the trafiic density computers MC, CC is identical tothat described above. The output of each computer is substantiallyproportional to traffic density for that direction of travel averagedover the integrating interval.

In this form of the invention, the balance and ratio detectors may bedesigned to include one or more split selections for each main directionof travel. For instance, two splits may be available favoring east-westtravel and two splits may also be available favoring north-south travel.One balanced split would favor each direction equally. In the first formof the invention, as shown in FIGURE 1, two splits are availablefavoring main street traffic and one balanced split is availablefavoring each direction equally. In the first form of the invention thecross streets are of only secondary importance, and no cuit is slightlydifferent in that it must select one of two the ratio detector circuitsis slightly different for the two forms of the invention.

Likewise, the design of the split seelctor slave relay circuit isslightly different in that it must select one of two splits for eachdirection of traflic, or a total of four splits. If traffic density isrelatively balanced, a fifth split favoring each direction equally isselected. Information received over four conductors is translated toinformation transmittable over two conductors and an existing groundconductor to local controllers.

Traffic density computer In both forms of the invention a trafiicdensity computer is provided for each direction of traffic. That is, onecomputer is provided to measure trafiic density on main street andanother is used to measure trafiic density on cross street, as inFIGURE 1. Or, one may be provided to measure traffic density on twoone-way east-west streets, and another to measure density on two one-waynorth south streets, as in FIGURE 2. Or, any combination may be used solong as density in the two intersecting directions is measured.

A block diagram of the units associated with each traffic densitycomputer is shown in FIGURE 3. A plurality of detectors D1, D2 areinstalled in the highway, one in each lane of traflic. The detectors maybe placed at the approaches to the intersection as shown in FIGURE 1, orin the various lanes of one-way streets as shown in FIG- URE 2, or inany configuration to count all the trafiic in that direction.

To assure maximum accuracy of the counter, each detector feeds into arespective blocking oscillator circuit as indicated by Bill-B05, whichreceives the signal from the detector and emits a pulse of uniform waveshape and substantially uniform amplitude.

The noisy output of the detectors, which has been noted on a cathode rayoscilloscope to include up to 14 impulses per actuation, is fed into theblock oscillators, which accept the first pulse and block out theremaining signal for 6 to 7 milliseconds. This wipes out the chatter.

The signal is next fed into a bistable multi-vibrator MV1 whose purposeit is to reduce two pulses to one. Each vehicle passing over a pressuresensitive detector puts out two pulses, one for each set of wheels.Since the purpose of the computer is to count vehicles per unit of time,it is desirable to reduce the two pulses to one so that the count willbe accurate.

Another reason for supplying both the blocking oscillators B01 to B05and the bistable multivibrator MV1 is to reduce each actuation to asshort a pulse as possible for preventing loss of one by overlapping oftwo pulsesarriving almost simultaneously from different detectors.

The bistable multivi'brator puts out a sharp pulse of short duration.This pulse is fed into a monostable multivibrator MVZ for which isemerges with a constant duration or width. It is desirable to send tothe integrator 11 pulses of uniform duration so that the integrator willgive each pulse equal Weight.

Pulses of uniform duration, one for each two axle vehicle, are fed intothe next stage, an instantaneous integrator 11. The time constant of theRC combination is 20 seconds, which is instantaneous only by comparisonto the long time integrator 12. The incoming pulses charge a capacitorwhich is allowed to drain off through a high resistance. The potentialof the capacitor is applied to the grid of a triode. A cathode followerprovides a potential across its cathode resistor proportional to therunning average of the number of vehicles counted during the previous 20seconds.

The short time integrator is provided for at least three reasons. First,a linear charging circuit is more easily applied to a short timeintegrator than a long time integrator. Second, an RC circuit with ashort time constant is more accurately charged from a short durationpulse than is an RC circuit with a long time constant. Third, in sometypes of traffic control application it is desired to know theinstantaneous density. An example of this cation is a singleintersection traffic control.

The potential from the short term integrator is applied to the long timeintegrator 12 which is an RC circuit with a longer time constant. Onenovel feature of this circuit is that its charging circuit is difierentfrom and independent of its discharge circuit and each may be set with adifferent time constant. In this embodiment its charging circuit may beset from 1 to 9 minutes in one minute increments.

The potential from the long-time integrator is applied to the grid of atriode. A cathode follower circuit provides a potential across itscathode resistor proportional to the running average of the number ofvehicles counted during the running interval. It will be understood thatno definitely timed interval, as such, is used here; the average is arunning average. As time transpires, new counts are added and old countsallowed to drain off so that the most current average is used. This is adistinct improvement over present equipment.

The long time integrator is required for control of a system ofintersections. A suflicient number of vehicles must be included in thesample to obtain an accurate picture of trafiic conditions. Short timechanges must not be allowed to effect a split change. But short timechanges must still be allowed to exert their influence on the long timetotal. Density from the long time integrator is useful in determiningcycle length, split, and offset.

The output potential from the long time integrator is applied to aPercent Trafiic Density meter VM which registers traflic density as apercent of the setting on an adjustment dial entitled vehicles per hourper lane at This latter adjustment permits'the computer to 'be used onhighways with widely different traflic densities.

Output is provided at output terminal OT for use by the split selector,or by a cycle length selector, an offset selector, a lane selector, orany of a variety of purposes.

A more detailed disclosure of the traffic density computer will be foundin United States patent application, Ser. No. 738,327, entitled TraflicLane Control, filed May 28, 1956.

Block diagram of ratio detector The potential from the two computers isapplied to a balance and ratio detector shown in block diagram in FIGURE4. The output potentials of the main street and cross street traflicdensity computers MC, CC are applied to the input terminals M, C of thegenerator PG. The potentials from the generator are then applied to thebalance detector BD where the higher potential may energize a relay toswitch said higher potential to a plurality of voltage dividers. Thelower potential is switched to one side of each ratio detector RBI toRD3.

Voltage dividers VD1 to VD3 reduce the higher potential by threedifferently reduced adjustable ratios. Each different potential isapplied to the grid of a ratio detector tube, the lower potential havingbeen applied to the other grid in each ratio detector tube. If anyreduced higher potential is sufficiently higher to outbalance the lowerpotential it energizes a relay which switches power to a controlconductor. The control conductor in turn energizes the proper relay inthe slave relay circuit SR.

The relative position of the three ratio detector relays determineswhich of four splits is energized at the local controller. Power toselect the proper split at the local controllers flows over lines M, Cfrom slave relay circuit SR.

The purpose of the slave relay circuit is to permit energization of thesplit selector relays in a number of local controllers. The slave relaysact as current amplification devices to reduce the load on the ratiodetector relays which are necessarily small because they are platecircuit relays.

A plurality of contact assembly and keys on a cycle timing dial at eachlocal controller effects the cycle split. A split selector relay makeseffective the proper contact assembly and dial key. A more detailedexplanation of the local split selector is found in another section.

Balance and ratio detector A circuit diagram of the balance and ratiodetector shown in block diagram in FIGURE 4 is shown in FIG- URE 5. Afive tube unit is employed in this embodiment with three of the tubesused as ratio detectors. In another embodiment more or fewer ratiodetectors may be employed without departing from the spirit of theinvention.

One ratio detector stage is employed for each independently adjustableratio desired. For instance, tube V3 detects the ratio of cross streetto main street trafiic. When traffic exceeds the preset ratio, tube V3energizes relay CR4. Contacts on relay CR4 actuate a control functioninthis case, a 50-50 split favoring cross street equally with main street.

A second ratio detector V2 is employed to detect the ratio of mainstreet to cross street traffic. When trafiic exceeds the preset ratio,tube V2 energizes relay CR1 which actuates a control function, here a60-40 split favoring main street.

A third ratio detector V is utilized to detect a higher ratio of mainstreet to cross street trafiic. When traflic exceeds a second, greaterpreset ratio, tube V5 energizes relay CR5 which actuates another controlfunction, here a 70-30 split favoring main street.

Thus the unit serves two functions: it discerns which direction oftrafiic is heavier, and it compares the ratio of heavy to light flowagainst one or two adjustable ratios to determine how much of thetraffic cycle shall be allocated to main street traflic.

Referring to FIGURE 5 in greater detail, the output of the main streettraffic density computer MC is fed in on pin P4, through potentiometerR1 and resistor R2 to the grid V461 of tube V4A. The output of the crossstreet traflic density computer CC is fed in on pin P7, throughpotentiometer R3 and resistor R4 to the grid V4G2 of tube V4B.

Tube V4 serves as a generator. The tube half which has the higherpotential impressed on its grid conducts more heavily. The cathode toplate current flowing through tube V4A increases the voltage rise acrossresistor R5 and increases the bias voltage on grid V1G1 of tube V1A. Thecurrent flowing through tube V4B increases the voltage rise acrossresistor R6 and increases the bias voltage on grid V1G2 of tube V1B.

The tube half VIA, VlB which has the higher positive potential impressedonits grid conducts more heavily and pull in relay CR2 or CR3 in itsplate circuit. If traffic is sufficiently heavier on main street thancross street, for example, relay CR2 will pull in closing contacts CR2-1and -2 and contacts CR2-4 and -5. L2 power is fed in on pin L2, throughthe contacts CR3-6 and -5, through contacts CR2-5 and -4, through line51 to contacts CR5-3, CR1-3, 'CR4-3. Now closed contacts CR2-1 and -2apply the potential arriving from the cross street computer CC throughpin P7 to the grids V5G2, V2G1, and V3G2 of the ratio detector tubesthrough grid resistors R7, R8, R9 associated with tubes V5B, V2A, V3B,respectively.

The output of the main street computer MC arriving through pin P4 is nowbeing fed through contacts CR3-3 and 2, through conductor 52 to thepotential dividers PD2, PD1 and PD3 associated with tubes V5A, V2B, V3A,respectively. The tap on each potential divider ap plies a reducedvoltage to the grids V5G1, V2G2, V3G1, respectively. The taps may be setfor the various ratios desired for split change. To illustrate furtherthe conditions enumerated in the first part of this section, potentialdivider PD1 associated with tube V2 may be set for any ratio between 1to l and 2.5 to 1. When the ratio of the main street to cross streettraffic exceeds the ratio set on potential divider PD1, relay CR1 isenergized pulling in split 60/40, for example. Note that the ratio seton the potential divider need not be the same as the split.

Potential divider PD3 associated with tube V3 may also be set for anyratio between 1 to 1 and 2.5 to 1. When the ratio of cross street tomain street traffic exceeds the ratio set on potential divider PD3,relay CR4 is energized pulling in split 50/50, for example. That is,even though cross street traffic is heavier than main, the split isawarded evenly, which actually gives main street an advantage and allowsmain street traffic free movement.

Potential divider PD2 associated with tube V5 may be set for any ratiobetween 1.5 to 1 and 2.5 to 1. When the ratio of main street to crossstreet trafiic exceeds the ratio set on potential divider PD2, relay CR5is energized pulling in split 70/30, for example.

Assume now that traffic is relatively heavy and that main street trafficexceeds cross street traffic by the ratio 1.25 to 1, for instance. Theleft half of balance detector tube V1 conducts pulling in relay CR2.Contacts CR21 and -2 close and apply across street computer potential togrids of V5G2, V261, V362, of ratio detector tubes V5, V2, V3. ContactsCR3-2 and -3 apply main street computer potential through potentialdividers PD2, PD1, PD3 to the other grids V561, V262, V361 of tubes V5,V2, V3, respectively, where the resultant ratios are compared. Tubehalves VZB and V3A will both conduct sufficiently to energize relays CR1and CR4, respectively, because the ratios of higher to lower potentialare within the ratios set on potential dividers PD1, PD3. With theenergization of relay CR1, contacts CR13 and -4 close feeding L2 powerthrough conductor 55 onto output terminal M associated with the 60/40split selector. Closure of contacts CR1-1 and 2 has no effect becausecontacts CR5-1 and -2 and contacts CR3-4 and -5 are open preventing L2power from reaching output terminal C on conductor 58.

Since relay CR4 is also energized, contacts CR4-3 and 4 are closedfeeding L2 power through conductor 57 onto terminal IB which is vacantin this application. Closure of contacts CR4-1 and 2 has no effectbecause line 56 is not energized because contacts CR5-1 and -2 are open,and because line 54 is not energized because contacts CR-3 and 5 areopen. Thus, no power is fed over line 58 to terminal C. No power is fedover line 59 to terminal OB because contacts CR5-3 and -4 are also open.Terminals IB, OB are used for inbound and outbound favoring offsets inanother application.

If cross street traffic had exceeded main street traflic, outputterminal C' and not M would have been energized. Contacts CRIS-4 and 5would have been closed allowing L2 power to energize output terminal Cover conductor 58. Also, output terminal M would not have been energizedbecause contacts CR2-4 and would have been open.

If now main street trafiic builds up heavier than cross street tratficuntil the ratio of main to cross street trafiic reaches 2 to l, forexample, relay CR5 will also be energized. Conduction through tube halfV5A will result from the increased potential developed by the mainstreet computer and fed in on pin P4, and applied through contacts CR3-3and 2, conductor 52, and potential divider PD2, to grid V5G1. Theincrease in potential causes tube half VSA to conduct, energizing relayCR5.

Relays CR1 and CR4, and therefore M, were already energized as trafiicincreased so that now all three ratio detector relays are energized.

With relays CR5, CR1, and CR4 energized, power is fed from line L2,through contacts CRS-l and 2, conductor 56, contacts CR1-1 and 2,contacts CR4-2. and 1, conductor 58, to output terminal C. With bothterminals 'C' and M thus energized, they make the fourth split elfectiveat the local controllers. This split may be set 70/ 30 in favor of mainstreet.

Output terminals 1B and OB are also energized but they are vacant inthis application.

Other balance and ratio detector circuits Various combinations ofbalance and ratio detectors may be assembled by one skilled in the artof electronics. For example, two combinations are shown in FIGURES 6 and7. The type designed depends on highway requirements and the number ofsplits required for each direction of trafiic.

FIGURE 6 illustrates a type of balance and ratio detector for a gridsystem. Two adjustable split changes are provided for each direction oftrafiic in addition to a balanced split favoring each direction equally.An independently adjustable greater and lesser voltage divider and ratiodetector is provided for each direction of traffic. With only slightchange in wiring, three of the adjustable ratios could be used for onestreet, and one for the other street.

If trafiic and geographic conditions are such that the same settingcould be used for both streets, a simplified version of the ratiodetectors could be assembled as shown in FIGURE 7. Only two adjustablesettings are provided and are used for both streets. That is, if thelesser voltage divider is set to eifect a split change when the ratio oftrafiic density on the two streets is 1.25 to 1, the split change willfavor main street when its traffic is 1.25 times heavier than crossstreet, or the split change will favor cross street when its traflic is1.25 times heavier than main street. Likewise, when the greater voltagedivider is set to effect a second split change when the ratio of trafficdensity on the two streets is 1.75 to l, the split change will favor thebusier street when its traffic is 1.75 times greater than the less busystreet. This simplified system I could be used advantageously with agrid system when the two groups of intersecting streets are of equaldignity.

Local cycle split controllers The split selector disclosed in thisinvention is designed for use in tratfic control systems using localtraffic signal controllers of the type described in pending UnitedStates patent application, Ser. No. 642,469, filed Feb. 26-, 1957,entitled Multiple Program Traflic Control Systems. However, the selectoris not limited to use with one specific type of local traific signalcontroller but may be used with any type which allows for theutilization of information or electrical energy furnished by theselector. Many controllers now in use may be adapted to permit themaster controller to vary their cycle split.

In one version of a split control mechanism, power is fed out onterminals M and/or C of the split selector shown in FIGURE 5. In theslave relay circuit SR shown in FIGURES l and 2 the current may beamplified so that a large number of local controllers may be controlled.Power flows .over one or more conductors in the interconnecting cable ICto each local controller LC connected into the system. The relay circuitSR is employed also to permit the transmission of four items ofinformation over a two conductor cable. The table below shows whichconductors are energized for the following conditions:

Main st. 1.5 times cross Within each local controller is a decodingnetwork which utilizes the information received on two conductors toenergize the selected cycle split. The relative position of two relayarmatures and contacts determines which split is elfective. A wiringdiagram of one such relay circuit is shown in FIGURE 8. FIGURE 8 is areproduction of part of FIGURE 7 of application, Ser. No. 642,469 notedabove. Relay positions will be explained with reference to conditionsshown in the table above and with reference to FIGURES 5 and 8.

Under condition 1 when cross street trafiic is equal to or less thanmain street trafiic, neither control relay CR2 nor CR3 is energized andneither conductor 'C' nor M is energized. Power is fed in on conductorL2, through contacts 108, 118, 1035, conductor 58, switch 705, to motor37 making split S1 eflective.

In condition 2 when cross street trafiic exceeds main street trafiic bya ratio greater than that preset on adjustable potential divider PD3, aspreviously explained, power is fed onto conductor C, which at the localcontroller'is wire 24, energizing local relay coil 10. This switcheslocal power from line L2 through contacts 108, 118', 11018, conductor58, switch 708, to motor 37 making split S2 effective.

Under condition 3 when main street traffic exceeds cross street traflicby -a ratio greater than that present on adjustable potential dividerPD], but not as great as that preset on potential divider PD2, controlrelays CR2, CR1, and possibly CR4 are energized. (CR4 has no efiectunder this condition because CR3 is de-energized preventing L2 powerfrom reaching the movable contact member, CR4-2). Power is fed ontoconductor M, which at the local controller is wire 25, energizing localrelay coil 11. This switches local power from line L2 through contacts108, 118, 1028, conductor 58, switch 705, to motor 37 making spilt S3effective.

In condition 4 when main street tralfic exceeds cross street trafiic bya ratio greater than that preset on adjustable potential divider PD2,control relays CR2, CR1, CR4 and CR5 are energized. Power is fed ontoconductors C and M, which at the local controller are designated 24, 25,energizing local relay coils 10 and 11. This switches local power fromline L2 through contacts 108, 1018, conductor 58-, switch 708, to motor37 making split S4 effective.

The invention includes a method of trafiic control including the stepsof: measuring a traflic characteristic, such as traffic density on boththe main highway and a typical cross street; developing and comparingsuch signals as electrical potentials representative of the two trafficcharacteristics or densities; determining the ratio of the signals, suchas the higher potential to the lower potential; and, changing a traflicfunction, such as split, based on the ratio of the potentials.

Thus, it is seen that the method of traffic control includes the stepsof: providing traflic signal lights S for "controlling tratfic flow intwo directions; electrically detecting a characteristic of traffic, suchas density, by utilizing traffic detectors D1, D2, D3 and D4; developingfirst and second electrical signals, such as electrical potentials, byutilizing computers MC and CC so that the signals are representative ofthe characteristic of traffic in the two directions; providing areference ratio by utilizing potential dividers PD1, PD2, or PD3;developing a third electrical signal from the first and secondelectrical signals when a given ratio relationship of the magnitudes ofthe first and second signals difiers from the reference ratio byapplying the first and second signals to tubes V2, V3 or V5, with one ofthe signals applied through potentiometers PD1, PD2 or PD3; and,utilizing the third signal for changing the operation of the trafficsignal lights S as by applying the third signal to relays CR1, CR4 orCR5.

The above description shows how the master cycle split selector choosesand energizes the proper split at the local controllers. A typical localcontroller will be explained more fully in the following section toillustrate its complete split function. The remainder of the circuitshown in FIGURE 8 will also be described.

Two dial controller A very thorough description of a local splitselector will be found in United States patent application, Ser. No.642,469, noted above. A short explanation will be made here tosupplement the teaching of the present invention.

FIGURE 9 represents part of a two dial local traffic signal controllerand is identical in function to the device shown in FIGURE 1 ofapplication, Ser. No. 642,469 noted above. The same numericaldesignations are used to avoid confusion. Dial 3 is the amber timingdial and is driven by synchronous motor 37 which is powered directlyfrom 60 cycle alternating current. Dial 3 carries on its surface 100slots each representing 1% of the periphery and 1% of a revolution ofthe dial. Dial 3 is geared to motor 37 so that it makes half arevolution in less time than the shortest split of the shortest cyclefor which the equipment is designed.

Into the slots in the face of dial 3 fit keys which may be displaced atany percent point in the cycle. Four types of keys are available, eachwith a projection located at one of four different locations measuredfrom the front of the slot. Four contact pairs are located above thedial, each pair operated by only one of the four key projections. Whenthe front contact pair is to be closed, for example, a key with aprojection in the front position is used. The table below shows thefunction of each dial key, its designation, and a sample dial setting.

DIAL 3 Setting,

Percent Function In the example illustrated in FIGURE 9, six keys arefitted into slots on dial 3, four keys having projections near the frontof the dial, and two keys having projections near the rear of the dial.The former keys are located at percentage times in the cycle at which itis desired to step the step switch and change the trafiic signalindications. The keys carry projections which close contacts which stepthe step switch once for each contact closure. The three keys 74, 78,S0, with projections in the front position are impulse keys. The key 31with a projection in the second position is a release key. Theirinteraction is explained in greater detail below.

Two keys, 32, 33, with projections located near the rear of dial 3 serveto open motor control contacts 32S, 338. As soon as the projection onkey 33, for example,

opens contacts 338, motor 37 is deenergized, dial drum 3 stalls, andcontacts 338 remain open. Closure of one of contact pairs 101$, 101$,1028, or 1038 on dial 2 is required to energize the motor 37 momentarilyto rotate dial drum 3 and cause the motor control contacts 338 to close,energizing motor 37 for another half revolution of the dial 3.

In like manner, the projection on key 32 opens the contact pair 328,deenergizing motor 37, which stalls dial drum 3 allowing contacts 328 toremain open. Dial 2 must then rotate until the projection on key 100momentarily closes the contact pair 100S energizing motor 37 throughline 57 and now-closed contacts 708. When motor 37 rotates dial 3 a fewdegrees contacts 328 again close permitting motor 37 to be energizeddirectly from line L2 for another half revolution of dial 3. Contacts705 are closed at the proper time by relay 70 being energized from lineL2 through contacts 498 closed by cam 49.

As noted above, two types of keys have projections near the front of thedial: impulse and release keys. Although neither is important to thepresent invention, they are included in the description. Impulse keys74, 78, 80, are developed around the dial at each point in the cycle atwhich the step switch is to be stepped to change the trafiic signalindication. The front contact 305 is closed by impulse keys 74, 78, tocause such stepping action.

To keep the camshaft 46 in step with dial 3 a release key 31 is used.Release key 31 closes contact pair 318 located adjacent to impulsecontacts 308. The release keys projection is to the rear of the impulsekeys projection. Release key 31 closes contacts 318 energizing ratchetsolenoid 48 which rotates camshaft 46 out of the main street greeninterval. The release key is used to terminate the main street greeninterval so that if camshaft 46 and dial 3 get out of step camshaft 46will remain in the main street green interval until dial 3 makes up toone revolution to again step the camshaft.

The camshaft 46 shown in part in FIGURE 9, carries cams 49, 59, andadditional cams (not shown) to operate switches to energize traificsignal lights S, as in FIG- URES 1 and 2.

Cam 59 allows closure of contacts 598 admitting L2 power to one contactof front contact pair 305. Closure of contacts 305 thus energizes theratchet solenoid 48 only when contacts 598 are closed. Contacts 595 arecontrolled by the action of cam 59 and are closed by the low section oncam 59. The low section of cam 59 corresponds to all of the cycle exceptthe main street green interval. During the main street green intervalthe high portion of cam 59 opens contacts 598 and makes impulse contacts308 ineffective. Closure of release contacts 318 by key 31 energizesratchet solenoid 48 because one contact of contact pair 318 iscontinuously connected to L2 power. The dial 2 and camshaft 46 are thuskept in step.

Split dial Dial 2 is constructed similarly to dial 3, Five keys 100,101, 101, 102, 103, have projections located in unique positions fromfront to rear, one projection on each key. Key located in slot 0 maymomentarily energize motor 37 out of its stalled condition during thecross street green interval. Any one of the keys 101, 101', 102, 103 maymomentarily energize motor 37 out of its stalled position during themain street green interval. Which of the latter keys is made effectivedepends upon which contact 1018, 101$, 102$, 1038 is energized which inturn depends upon the position of relay contacts 10S, 11S, and 11S.

Relay contact is maintained in the position shown by its own springpressure and is urged into its other position when coil 10 is energizedthrough conductor 24 from interconnecting conductor C. Relay contacts118, 118', are maintained in the position shown by their own springpressure and are urged into their other position when coil 11 isenergized through conductor from interconnecting conductor M.

Dial 2 rotates continuously at a uniform speed determined by synchronousmotor 60, energized by an alternating voltage VF which may vary infrequency from 40 to 120 cycles per second. The frequency is constantover a period and is varied by or from a master controller toeffectively change the length of cycle of trafiic signal change. Thisfeature is covered in United States patent application, Ser. No.642,469, noted above.

The purpose of dial 2 is to time the termination of the cross streetgreen interval near the zero point in the cycle, and to time thetermination of the main street green interval at the percentage split inthe cycle as selected by the Master Controller. Keys on dial 3 actuallyinitiate and terminate the intervals while the keys on dial 2 time thestart of dial 3. The table below shows the function of each key on dial2, its designation, and a sample dial setting. The keys on dial 2actually time the beginning of the end of their interval.

DIAL 2 Setting,

Percent Function One rotation of dial 2 times one rotation of dial 3 andone complete change of traffic signals. The first key on dial 2, key100, closes contacts 100$ momentarily which energize motor 37 out of itsdeenergized condition caused by the opening of contacts 328. The latterfour keys on dial 2, keys 101, 101, 102, 103, close contacts 101$, 101$,102$, 103$, momentarily, one of which energizes motor 37 out of itsdeenergized condition caused by the opening of contacts 338. At anytime, only one of the four latter contacts is energized and is eifectiveto start dial 3 into the second half of its cycle. The effective contactdetermines how the cycle will be split and is energized through relaycontacts controlled by the split control conductors C, M.

If the cycle is to be split 50-50, for example, key 101 located in slot50 must be effective. Key 101 is made effective when contact 1015 isenergized from an L2 source through contacts 105 and 118'. Thiscondition exists when relay coil 10 is energized and coil 11 is notenergized. Thus, to make split S2 effective, control conductor C must beenergized, causing the traffic cycle to be divided 50% to main streetand 50% to cross street.

Energizing control conductor M and not C makes split S3 effective. Powerflows from conductor L2 through contacts 108, contacts 115, contacts1028, line 58, contacts 708, to motor 37.

Solenoid coil 70 is energized only during the cross street greeninterval to close contacts 708 and make line 57 and contacts 1008effective. This circuit permits contacts 1008 to start motor 37 out ofits stalled condition during the cross street green interval.

Energizing control conductors C and M energizes both relay coils 10 and11 and makes split S4 effective. Power flows from conductor L2, throughcontacts 10S, contacts 118', through contacts 1015, line 58, contacts708, to motor 37.

Split S1 is effective with neither control conductor C nor M energized.Power flows from conductor L2, through contacts 108, contacts 118',through contacts 1018, line 58, contacts 708, to motor 37.

Latch relays may be used instead of the normal relays 10, 11 used toenergize one or another split contact. When the interconnectingconductors C or M are energized they energize the main coil of theirassociated relays 10, 11. Contacts 105, 118, or 118 do not close untilthe release coils not shown) are energized, pulling a latch away fromthe main armature, permitting the main armature to act on its contacts.

The release coils are energized during a portion of the cycle when atransfer in splits would be least disruptive of normal operation. Therelease coils may be energized by contacts 49S which are closed onlyduring the cross street green interval. This prevents disruption of thetraffic signal cycle during switching of the splits.

Function selector Broadly, the invention provides means for selecting aparticular mode of operation of an apparatus capable of operating inseveral different manners. The use of the balance and ratio detectorsdisclosed in this invention is not limited to split selection or totraffic control. As stated in a prior section, the output of the trafficdensity computers can be used for a variety of purposes such as splitselection, offset selection, cycle length selection, lane control, orany other purpose. Likewise, the ability of the balance and ratiodetectors to discern which of two potentials is higher and by what ratiois useful for split selection, offset selection, cycle length selection,lane control, or any other purpose. Therefore, the balance and ratiodetector assembly may well serve as a function selector for a variety ofapparatus.

Having described the invention in one or more forms or arrangements, itwill be evident to one skilled in the art that modifications or changesmay be made without departing from the spirit of the invention.

Having thus described my invention, I claim:

1. A method of adjusting traffic flow comprising the steps ofcontinuously electrically measuring a characteristic of traffic in onedirection of traffic fiOlW and a characteristic of traffic in a seconddirection of traffic flow, generating an electrical potential indicativeof each said characteristic, electrically comparing the two potentialsto find the higher, electrically reducing the higher simultaneously by afirst and a second reduction ratio, electrically comparing the variouslyreduced higher potentlal with the other potential, providing traflicsignal lights for controlling traffic flow in said two directions,allocating a first adjustment of trafiic flow to said directions oftraffic flow by changing the operation of traffic signal lights when thehigher potential reduced by the first ratio is greater than the otherpotential, and allocating a second adjustment of traffic flow bychanging the operation of trafiic signal lights when the higherpotential reduced by the second ratio is greater than the otherpotential.

2. A method of traflic control for controlling traffic fiow in at leasttwo directions of trafiic flow, comprising the steps of providingtraffic signal lights for controlling trafiic How in said twodirections, developing electrical signals representative of acharacteristic of traffic in said two directions of traflic flow,electrically reducing said characteristic signals to a ratiorelationship of said characteristic signals, electrically comparing saidratio relationship with a reference representative ratio relationship oftraffic characteristics, and controlling the traffic flow in said twodirections by changing the operation of said traffic signal lights whensaid ratio relationship is different from said reference representativeratio relationship.

3. A method of trafiic control for controlling trafiic flow in at leasttwo directions of traffic flow and comprising the steps of: providingtrafiic signal lights for controlling traffic flow in said twodirections; electrically detecting a characteristic of traflic in saidtwo directions; developing first and second electrical signals havingmagnitudes respectively representative of said characteristics oftraffic in said two directions; providing a refer ence ratio; developinga third electrical signal from said first and second electrical signalswhen a given ratio relationship of the magnitudes of said first andsecond signals differs from said reference ratio; and, utilizing said 17third signal for changing the operation of said traflic signal lights.

4. A method of traflic control for controlling trafi'ic flow in at leasttwo directions of trafiic flow and comprising the steps of: providingtraffic signal lights for controlling traffic fioiw in said twodirections; providing traflic control circuit means for changing theoperation of said trafiic signal light; electrically detecting acharacteristic of traffic in said two directions; developing first andsecond electrical signals having magnitudes respectively representativeof said characteristics of traffic in said two directions; providing areference ratio; electrically comparing a given ratio relationship ofthe magnitudes of said first and second signals with said referenceratio; developing a third electrical signal when said ratio relationshipis different from said reference ratio; and, applying said third signalto said trafiic control circuit means for changing the operation of saidtraffic signal lights.

No references cited.

0 THOMAS B. HABECKER, Primary Examiner

